Optical fiber

Summary

An optical fiber, or optical fibre in Commonwealth English, is a flexible, transparent fiber made by drawing glass (silica) or plastic to a diameter slightly thicker than that of a human hair. Optical fibers are used most often as a means to transmit light between the two ends of the fiber and find wide usage in fiber-optic communications, where they permit transmission over longer distances and at higher bandwidths (data transfer rates) than electrical cables. Fibers are used instead of metal wires because signals travel along them with less loss; in addition, fibers are immune to electromagnetic interference, a problem from which metal wires suffer. Fibers are also used for illumination and imaging, and are often wrapped in bundles so they may be used to carry light into, or images out of confined spaces, as in the case of a fiberscope. Specially designed fibers are also used for a variety of other applications, some of them being fiber optic sensors and fiber lasers. Optical fib

Official source

https://en.wikipedia.org/wiki/Optical_fiber

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Microwave-to-Optical Transduction with Gallium Phosphide Electro-Optomechanical Devices

Simon Benjamin Klaus Hönl

Quantum computing is one of the great scientific challenges of the 21st century. Small-scalesystems today promise to surpass classical computers in the coming years and to enable thesolution of classically intractable computational tasks in the fields of quantum chemistry,optimization, cryptography and more.In contrast to classical computers, quantum computers based on superconducting quantumbits (qubits) can to date not be linked over long distance in a network to improve their computingcapacity, since devices, which preserve the quantumstate when it is transferred from onemachine to another, are not available. Several approaches are being pursued to realize such acomponent, one of themost promising to date makes use of an intermediary, micromechanicalelement that enables quantum coherent conversion between the information presentin the quantum computer and an optical fiber, without compromising the quantum natureof the information, via optomechanical interaction. This approach could allow fiber-opticquantum networks between separate quantum computers based on superconducting qubitsin the future.In this work a platformfor such a microwave-to-optic link was developed based on the piezoelectricmaterial gallium phosphide. This III-V semiconductor offers not only a piezoelectriccoupling between the electric field of a microwave circuit and a mechanicalmode, but also awide optical bandgap E_g = 2.26eV which reduces nonlinear optical absorption in the deviceand a large refractive index n(1550nm) = 3.01 which allows strong optical confinement atnear-infrared wavelengths.Importantly and in contrast to other approaches with gallium phosphide, an epitaxiallygrown, single crystal thin film of the material is integrated directly on a silicon wafer withpre-structured niobium electrodes by direct wafer-bonding. This opens up the possibility ofintegrating the device design presented here directly with superconducting qubits fabricatedwith this material system.A microwave-to-optical transducer design was simulated and fabricated in the galliumphosphideon-silicon platform. The device was found to exhibit large vacuum optomechanical couplingrates g0/2 pi ~ 290kHz and a high intrinsic optical quality factor Q >10^5 while at the same timepermitting electromechanical coupling to a microwave electrode. Coherent microwave-toopticaltransductionwas shown at room temperature for this device and the electromechanicalcoupling rate could be extracted from a model derived by input-output theory.The electromechanical coupling between the electro-optomechanical device and a superconductingqubit was estimated to be g/2 pi = O(200kHz) which indicates that strong couplingbetween the here presented device and a superconducting transmon qubit is achievable.In addition, superconducting microwave cavities with high quality factor at single photonenergy Q ~ 5x10^5 were fabricated and measured to verify that fabrication process of themicrowave-to-optical transducer is compatible with high-quality superconducting microwavecircuits.

EPFL2021

Multimode fiber optical imaging using wavefront control

Nicolino Stasio

Optical microscopy enables us to observe at high resolution and with a large field of view objects otherwise invisible for the naked eye. This is why it is becoming a fundamental tool in biology and in diagnostics, where observation at cellular level can tell about the health status of a tissue. At visible wavelengths, light undergoes scattering when propagating through tissues, limiting the imaging depth to the first cellular layers of a biological sample. Endoscopic approaches allow the bypass of the scattering layers and move the accessible volume centimeters inside tissues, ideally keeping large field of view and high-resolution capabilities. In this thesis we explore the combination of wavefront control and ultrathin multimode optical fibers to develop a new family of endoscopes able to generate images with micrometric resolution being, at the same time, minimally invasive. We demonstrate that a variety of imaging techniques can be implemented in optical fiber-based endoscopy, maximizing the amount of information that can be collected through a few hundreds of micrometers-thick probe. Firstly, we describe digital phase conjugation (DPC), which is the utilized wavefront shaping technique to convert a multimode optical fiber in an ultrathin endoscope. The use of DPC in synergy with multimode optical fibers resulted in ultrathin probes able to perform fluorescence imaging, photoacoustic imaging, and multiphoton imaging. Moreover, we show that using saturation excitation of fluorescent samples we can beat the resolution limit imposed by the numerical aperture of the optical fiber and obtain optical sectioning. In the first part of the thesis we describe which steps have been performed towards the implementation of these techniques. In the second part, we exploit coherent fiber bundles as imaging probes. This kind of fiber is typically utilized in endoscopy, but their resolution is limited by the distance between the fiberâs cores. Here we show two techniques - one based on DPC and a second based on statistical properties of speckle patterns - to obtain images with a better resolution than the one imposed by the core-to-core spacing, both relying on a unique property of multicore fibers: the memory effect. We also accomplished complex pattern transmission through multicore fibers with high resolution. Overall, the presented work provides new insights in imaging through optical fibers based on wavefront shaping techniques, opening up pathways for addressing current issues in this research field.

EPFL2017

Optical fibers have reshaped the technological landscape, from optical networks and high-speed data communication to in situ imaging and non-invasive surgery methods. The revolution allowed by these fibers has been made possible by its fabrication method, the thermal drawing process, which combines high scalability and nanoscale fabrication accuracy. Despite tremendous successes, silica step-index and photonic crystal fibers have held intrinsic limitations due to their mechanical rigidity and fragility, limiting their possible applications . There is however an increasing demand for optical fibers that could guide light efficiently while sustaining large deformations in fields like robotics, smart textiles and the automotive world. Other fields in sensing, helath care or advanced textiles could benefit from soft fibers that could display tunable optical effects. Techniques like lithography and molding have proven valuable to fabricate complex elastomeric photonic fibers, but their limited scalability intrinsically limits their use in several fields of application. On the other hand, scalable fabrication techniques like extrusion guarantee the desired throughput but fail to deliver the architectural complexity required to realize softfibers advanced optical properties. In this thesis, we propose to exploit the thermal drawing process to realize different types of soft and highly stretchable optical fibers, from the classic step-index architecture to 1D photonic crystal fibers, liquid core fibers and 2D photonic crystal fibers. To achieve this overall objective, we first establish a theoretical framework to evaluate the material requirements from the rheological, optical and mechanical point of view. After selecting the materials, we develop a step-by-step fabrication process that starts from the material pellets and ends with the fabrication of meters of elastomeric photonic fiber via thermal drawing. We then move on to fully characterize the optical and mechanical properties of the fibers and design several fiber-based devices with specific optical effects. More specifically in Chapter 2, we demonstrate the materials selection, innovative fabrication process, and the optical and mechanical characterizations to realize a soft optical wave-guide based on a step-index design. To highlight its optical and mechanical performance, we demonstrate a strain sensing sport gear that integrates this newly developed fiber. In chapter 3, we go one step further in the control over feature size by going about a similar demonstration for a 1D photonic crystal fibers based on all-elastomeric materials, with feature sizes down to sub-100 nm. We show in particular a mechanochromic fiber that can reversibly change color upon stretching. In Chapter 4, we propose a series of other fiber architectures based on our scientific and technological achievements that include a multicore stretchable step-index fiber that form the basis of an advanced demonstrator of a soft fiber with multiple channels and functionalities found in endoscopes. We also present preliminary results on a liquid-core step index fiber, and a stretchable 2D photonic crystal fiber, that pave the way towards highly complex and high-performance soft optical fiber devices.

EPFL2021

Microwave-to-Optical Transduction with Gallium Phosphide Electro-Optomechanical Devices

Simon Benjamin Klaus Hönl

EPFL2021

Multimode fiber optical imaging using wavefront control

Nicolino Stasio

EPFL2017